1. Field of the Invention
The present invention relates to the tools and methods for producing fluids from within the Earth. More particularly, the present invention relates to a pressure differentially operated production valve.
2. Description of the Prior Art
In the industrial context of petroleum production and earth boring, pressure differentially operated production valves are flow control devices positioned downhole within a petroleum production tube. One purpose for which the valve is used is for isolating a petroleum production zone during the well completion process. After one or more annulus isolation packers are set above or below or both relative to the production zone, the differential valve is opened to permit well fluid flow into the production tube. The valve is opened by elevated fluid pressure within the production or completion tube after the packers are set and the production zone is isolated from the atmospheric surface.
Prior art valves are opened by a pressure value that is the differential between the tubing bore pressure and the well annulus pressure. Consequently, the magnitude of fluid pressure essential for opening the valve is dependent on the annulus pressure in the immediate proximity of the valve. However, because the production zone is isolated from the atmospheric surface head by the packers above the production zone, the production zone pressure is not always known. In isolation, the production zone pressure may be considerably greater or less than the surface head. This unknown in the production zone pressure is translated to an unknown pump pressure required to open the valve.
It is therefor, an object of the present invention to provide a downhole production valve having an operating pressure that is independent of the production zone pressure.
Also an object of the invention is a downhole valve that is operatively responsive to the annulus pressure above a predetermined uphole packer.